528 GENEEAL CHARACTERS OF REPTILES. 



in Birds. The members do not in general present anything very 

 remarkable. Sometimes they are abruptly terminated at the 

 end, and can only serve to push the animal forward, as in Land 

 Tortoises for example ; sometimes they are terminated by slender 

 fingers, and furnished with claws, which allow the animal to hook 

 itself on by inequalities of the surface, and to climb with facility ; 

 the feet of many Lizards are formed in this way, and those of tro- 

 pical climates are described as exhibiting astonishing agility in 

 climbing, running up perpendicular surfaces, and springing from 

 one point to another with remarkable ease and certainty. In other 

 instances there is at the extremity of the fingers a particular ar- 

 rangement, which is singularly favourable to this kind of move- 

 ment ; thus, among the Geckos (Fig. 323) the fingers are very 

 much expanded towards the end, and furnished underneath with 

 little folds of skin, which appear to perform the function of 

 suckers, and which permit these hideous Reptiles to ascend along 

 the smoothest walls, and even to walk in an inverted position 

 upon ceilings. There are also some Reptiles whose fingers are 

 opposable, almost as in the hand of Man ; in fact, among Chame- 

 leons (Fig. 322) they are united in two sets, which spread out 

 and approach each other, like the arms of a pair of pincers, and 

 which enable these animals to take a firm hold of the branches 

 on which they rest; Chameleons have also a prehensile tail, 

 which makes them essentially climbing animals. Finally, in 

 other Reptiles adapted to a life more or less aquatic, the fingers 

 are sometimes webbed, as is seen in the posterior feet of the 

 Crocodile ; and perhaps still more strikingly amongst the fresh- 

 water Tortoises ; or are even transformed to a kind of flattened 

 paddle, unfit for walking, but very favourable for swimming. The 

 Turtles (Fig. 318) are the only Reptiles which at the present time 

 possess this last form of structure ; but at more remote periods 

 of the geological history of the globe, our seas were peopled with 

 large animals provided with similar paddles, and presenting as 

 to the rest of the body great resemblance to Lizards and Serpents ; 

 some of these skeletons have been discovered in the fossil state, 

 and they have been designated by the names of Ichthyosaurus 

 (Fig. 320) and Plesiosaurus (Fig. 321). 



